Current supply apparatus



April 1952 J. R. STONE 2,592,615

CURRENT SUPPLY APPARATUS Filed Aug. 19, 1949 2 SHEETSSHEET l IllINVENTOR ATTORNEY April 15, 1952 STONE 2,592,615

CuR RENT SUPPLY APPARATUS Filed Aug. 19, 1949 2 SHEETSSHEET 2 INVENTORJOHN RHYMO/Vfi 870/345 ATTORNEY Patented Apr. 15, 1952 UNITED STATESPATENT OFFICE CURRENT SUPPLY APPARATUS John R. Stone, West Orange, N. Jassignor to Bell Telephone Laboratories, Incorporated, New York, N. Y.,a corporation of New York Application August 19, 1949, Serial No.111,199

12 Claims. 1

This invention relates in general to rectifier type current supplysystems and more particularly, to self-controlled, output-regulatedrectifier apparatus.

Heretoiore, there have been devised innumerable systems for rectifyingvoltage from an alternating source to supply direct current to a load.Many of such systems have included means for regulating the output ofthe rectifier in some given manner, providing constant current orconstant voltage output to the load. With such systems, however, it isdesirable to provide a simple apparatus involving a minimum number ofelectron discharge devices, and to eliminate the need for mechanicallyoperated servo-controlled circuits with their accompanying moving parts.In accordance with the invention, regulated rectifier type powersupplies are provided embodying a controller system having a minimumnumber of electron discharge devices and associated cir- V cuitrytherefor, and with no moving parts.

In summary, the invention employs a resistance element having amagnitude varying in accordance with a low voltage, low power, controlsignal supply thereto. In one circuit according to the invention, thisvariable resistance element is inserted as one of the arms of aphaseshifting bridge circuit, controlling the relative phase of avoltage supplied to the grid-cathode circuit of a gaseous dischargerectifier system. The control signal for the variable resistance elementis derived, through an amplifier, from the output of the gaseousdischarge rectifier. A rectifier system employing gaseous dischargerectifiers in somewhat similar manner is shown in copending applicationof F. W. Anderson, Serial No. 111,208, filed August 19, 1949.

In other circuits, according to the invention, the variable resistanceelement is used to provide control through an impedance inserted betweenthe source of alternating voltage and a conventional rectifierapparatus; in still another circuit the variable resistance elementitself produces a voltage drop in series between the alternating voltagesource and the rectifier. In the latter two circuits, the control signalfor the variable resistance element may be obtained from the output ofthe rectifier system.

The principal object of the invention is to provide a current supply orrectifier apparatus hay-- ing its output regulated in accordance with aparameter of the rectifier output and employing a non-mechanical,variable resistance control element.

The objects of the invention may be realized by the means described indetail in the following specification:

Fig. 1 shows an electric schematic of a variable resistance elementaccording to the invention;

Fig. 2 shows an electric schematic of a preferred embodiment of thecontrolled rectifier system according to the invention;

Fig. 3 shows an electric schematic of a further embodiment of acontrolled rectifier system according to the invention; and

Fig. 4 shows an electric schematic showing a still further embodiment ofa controlled rectifier system according to the invention.

Referring now to Fig. 1, a variable resistance element according to theinvention is here shown. A source of alternating voltage I is in serieswith a circuit to be controlled 2, the latter having some value ofimpedance. Completing the series circuit between the source ofalternating voltage I and controlled circuit 2, are vertices a and b, ofthe variable resistance element. A portion of the variable resistanceelement is composed of four unidirectional conductors l, 8, 9 and it!connected in a bridge circuit 3 and having vertices at points a, b, cand d. The polarities in which the unidirectional conductors will permita flow of current will be later explained. The unidirectional conductorsl, 8, 9 and Ill are shown as metallic disc rectifiers employing somesemi-conductive material such as selenium, copper oxide, or bariumtitanate, but may be of any convenient type such as thermionic dischargetubes or the like. Metallic disc rectifiers so employed are commonlyknown as varistors, and display a low resistance to the passage ofcurrent in a given direction known as the forward direction, and arelatively high resistance to the passage of current in the opposite orback direction. The limit of values of high and low resistance of suchvaristors depends, inter alia, upon the physical properties of thesemi-conductors employed.

A thermionic discharge tube 4 having a cathode, grid and anode is shown;the anode-cathode circuit of this tube is connected between vertexpoints 0 and d. The controlling signal input is supplied to thethermionic discharge tube 4 between terminals 5 and 6.

In general, the variable resistance element operating between points aand b is so connected as to modulate or control the flow of alternatingcurrent from the supply source I as it passes to the controlled circuit2, in accordance with the magnitude of voltages found at the controlsignal input terminals 5 and 6.

In the ensuing discussion, the flow of current in 4, a high resistancebeing offered to current flow from d to a. Assuming that the cathode ofthermionic discharge tube 4 is properly energized, the current flowpasses from its anode to the cathode and thence to point e. A resistanceto the flow of electrons from the anode to the cathode of discharge tube4 is developed, having a magnitude dependent upon the anode resistanceof discharge tube 4. This, in turn, depends upon the grid-cathodevoltage of discharge tube 4. A more negative voltage on terminal 5 withrespect to 6 increases the anode resistance; a less negative voltagedecreases the anode resistance. The current will then pass from vertex 0to a through varistor H3 which offers a relatively low resistance to thepassage of current in this direction, to a. Assuming, therefore, thatvaristors- 8 and In offer a negligibly low resistance to current flowfrom points I) to d, and c to a, respectively, the resistance presentedbetween vertices b and a will depend substantially upon the anoderesistance of thermionic discharge tube 4. This anode resistance hasbeen shown depending upon the control grid-cathode voltage applied tothe tube 4.

Uponthe subsequent half cycle of output voltage from the alternatingsource i, point b will become negative and controlled circuit 2 will bepositive. The current will flow from the positive lead of source Ithrough controlled circuit 2 to point a. A high back resistance to theflow of current will be offered from point a through varistor I9, but alow forward resistance will be presented to the flow of current throughvaristor 9 to d. Accordingly, the current passes from point a to pointd, thence to the anode of discharge tube 4. As before, the current willpass from anode to cathode of thermionic discharge tube 4; a resistancewill be presented to this flow depending upon the relative polarity andmagnitude of this control signal voltage provided at points 5 and 6. Thecurrent flow will pass from the cathode of discharge tube 4 to point 0and through the low forward resistance offered by varistor I from c to band thus to the negative side of alternating source I.

If the minimum resistance presented by the discharge tube 4 is notsufficiently low for the proper control 01 current to the circuit,additional thermionic discharge tubes such as 4-11 and 4-2) may beconnected in parallel with discharge tube 4 and in sufficient number sothat the net resistance presented by the combination of tubes can bemade to obtain any desired value. If a higher resistance is requiredthan may be obtained with thermionic discharge tube 4 as a triode, thehigher anode resistance oifered if thermionic discharge tube 4 is apentode may be utilized.

Referring now to Fig. 2, a rectifier employing a variable resistanceelement is here shown. A source of alternating current is supplied toterminals II and i2. thence to the primary of a transformer 13.

Transformer i3 supplies alternating voltages to two gaseous dischargerectifier triodes l4 and I5 connected-in full wave. Rectifiers l4 and 15may be of the thyratron" type, a name generally indicative ofgrid-controlled gaseous discharge rectifiers. The output of the fullwave thyratron rectifier is supplied between the center tap of thesecondary of transformerl3 and the common cathodes of thyratrons i4 andI5, to theload I6.

The amount of current passed by the thyratrons i l and i5 will bedetermined by the phase of the grid-cathode voltage with respect to theanode-cathode voltage of the thyratrons. When the grid-cathode voltageapplied to thyratrons I4 and I5 is exactly in phase with theanodecathode voltage, the thyratrons pass the maximum current. As thephase of the grid-cathode voltage is shifted more and more from theinphase to an out-of-phase condition with respect to the anode-cathodevoltage, the current passed by the thyratrons is correspondinglyreduced. When the grid voltage and anode-cathode voltage are degrees outof phase, no current will be passed by the thyratrons l4 and i5 and theoutput will be zero. Grid-controlled thyratrons can be considered as hotcathode, phase sensitive, rectifier tubes, in which a grid or a controlelectrode has been inserted. This grid serves a function analogous tothat of a control grid in an ordinary vacuum tube. However, the grid isable only to initiate the flow of anode current; once current hasstarted, the magnitude of current flow is not fixed by the gridpotential nor is any change of the grid potential able to stop the flowof current. Current can be stopped by making the anode zero or negativewith respect to the cathode for a short interval of time. ,By shiftingthe phase of the grid-cathode voltage, the time at which theanode-cathode current is initiated can be shifted. The time of the cycleduring which current passes will therefore be controlled by shifting thepoint at which the anode-cathode current is initiated.

. The alternating voltage supplied to terminals H and I2 is alsosupplied to the primary of a transformer I8. The secondary of thistransformer I8 is included as two arms of a phase shifting bridge; onearm extends between a: and y, and a second arm between 1/ and z. A thirdarm is presented between points b and a, which is the variableresistance element previously described in connection with Fig. 1; afourth arm between points a and o: comprises a reactance .19 which maybe a capacitance. The output vertices y and a of the phase shiftingbridge are connected to the primary of a transformer 20.

Two parallel branches are supplied for the fiow of current from thesecondary of transformer 18. Thus, that portion ofthe secondary voltageof transformer l8 developed between points a: and y is supplied throughcapacitance is to the primary of transformer 20. The phase of the supplyvoltage will thus be shifted, providing a leading current to theprimaryof transformer 26 in the first parallel branch. That portioniofthe secondary voltage of transformer I8 between points 1/ and 2 will besupplied through the variable resistance element at points I) and a;thenceto the primary of transformer 20 in the second parallel branch.The flow of current through this second parallel branch hassubstantially no shift in phase, as the variable. resistance elementintroduces no reactance in this branch. x

The current flowing through the primary of transformer 20 will be inpart the leading or outof-phase current supplied through capacitance I 9and in part, the in-phase current supplied to the variable resistanceelement. If the resistance between points I) and a, the variableresistance element, is made very small, the primary of transformer 20will be supplied substantially with an in-phase voltage. As theresistance between points a and 12 increases, the resistance of thevariable resistance element increasing, the proportion of the in-phasecurrent in the primary of transformer 20 becomes increasingly less.Thus, the ratio of out-ofphase current supplied through the capacitanceI9 becomes higher, and transformer I9 is supplied a voltage having alarger out-of-phase component.

The grid-cathode voltage of the thyratrons I4 and I5 is obtainedrespectively on either side of the tapped secondary winding oftransformer 20. It will be seen that the phase of the gridcathodevoltage of thyratrons I4 and I5 will depend upon the resistancepresented by the variable resistance element between points I) and a.

A voltage divider 2| i connected across the output of the thyratronrectifiers I4 and I5; a voltage proportional to the output voltage willbe obtained across segment 2I-a of the voltage divider 2I. Assuming thatswitch 22 is made to its left-hand contact, a voltage proportional tothe output voltage is presented to a direct coupled amplifier utilizinga thermionic discharge tube 24. A fixed bias supply 23 is employed toneutralize a portion of the steady output voltage component of thethyratron rectifier in the grid-cathode circuit of amplifier tube 24.Output voltage variations of the thyratron rectifiers will appearbetween the grid and cathode of the amplifier tube 24. These variationswill be amplified by tube 24 and will appear across the anode resistance25. The amplified variations are supplied thence to the grid-cathodecircuit of thermionic discharge tube 4; corresponding to discharge tube4 in Fig. 1. As in Fig. l, discharge tube 4 controls the magnitude ofthe resistance presented between points 1) and a of the variableresistance element.

For example, let it be assumed that the output voltage from thethyratrons I4 and I5 has increased. Such a voltage increase is reflectedas a proportionately increasing voltage across the voltage dividersegment 2I-a. The steady component of the voltage across 2 I-a isneutralized or overcome by the bias battery 23 to the extent that aproper operating bias is supplied the grid-cathode circuit of amplifiertube 24. The voltage increase across divider segment 2I-a will cause anincreasingly positive voltage on the grid with respect to the cathode oftube 24. This increasingly positive voltage in turn causes a rise in theanode current of amplifier tube 24; the voltage drop across the anoderesistance 25 is increased and the anode voltage will drop. As thepotential at the cathode of thermionic discharge tube 4 is fixed at theposi-- tive end of supply battery 26, the decreased anode potential ofamplifier tube 24 will render the grid of thermionic discharge tube 4more negative. A the grid of the discharge tube 4 becomes more negative,the resistance introduced by the variable resistance element betweenpoints I) and a increases as previously explained. The primary oftransformer 20 will be in turn presented with a voltage increasinglyout-of-phase and the grid-cathode voltages applied to the thyratrons I4and I5 will also be shifted out of phase with regard to theiranodecathode voltages. The output of the thyratron rectifiers I4 and I5will thus be reduced, compensating for or minimizing the originallyassumed increase in output voltage.

Similarly, it may be shown that a decrease in output voltage isreflected across the segment 2I-a of the voltage divider 2I and willresult in an an-phase shift of the grid-cathode voltage of thyratrons I4and I5 to minimize the decrease of output voltage of the thyratronrectifiers.

A resistance I! is inserted in series with the output of thyratronrectifiers I4 and I5 to the load. Assuming now, that switch 22 is madeto its right-hand contact, the voltage developed by the load currentacross resistance I! will be presented in series with the fixed biassupply 23 to the grid-cathode circuit of amplifier tube 24. Changes inload current vary the voltage drop across resistance [1. Inasmuch as aportion of the voltage developed by normal load current acrossresistance I I can be neutralized by the bias supply 23 to provide aproper bias to tube 24, voltages representative of changes in loadcurrent will be developed between the grid and cathode of amplifier tube24.

It may be shown, for example, that an assumed increase in output currentwill increase the voltage drop across resistance II; the grid ofamplifier tube 24 will become more positive. This increased positivegrid voltage causes a rise in the anode current of tube 24, in turnproviding a more negative voltage on the control grid of thermionicdischarge tube 4 with respect to its cathode. As has been demonstrated,this causes an increase in resistance of the variable resistance elementbetween points b and a and a consequent out-of-phase shift in thegrid-cathode voltage of thyratrons I4 and I5 results. The out-of-phaseshift reduces the output of thyratrons I4 and i5, and compensates for orminimizes the assumed increase in load current.

It may similarly be shown, a decrease in load current will ultimatelyprovide an in-phase voltage shift in the grid-cathode supply voltage tothyratrons I4 and I5, increasing the output current and compensating foror minimizing the assumed decrease in load current.

It follows that by operation of the switch 22, it is possible tomaintain the output of the thyratron rectifier system either at aconstant output voltage or at a constant output current value.

Referring now to Fig. 3, a source of alternatin current is presented toterminals II and I2. Terminal II is connected in series with a fixedimpedance 28, having a given value, to the primary of a transformer 21.The secondary of transformer 21 is connected to the input vertices of aconventional bridge rectifier 29. The output vertices of rectifier 29connect to a load 30. While rectifier 29 is shown as a full wave,metallic disc rectifier, many types of conventional rectifierarrangements may be used herein.

The variable resistance element is connected between points I) and a inseries with the fixed impedance 28, and in parallel with the primary oftransformer 27. By varying the resistance offered between points I) anda, at least a portion of the current drawn through the fixed impedance28 can be caused to vary in a. similar manner. The subsequent voltagedrop presented by impedance 28 to the transformer 27 can thus be made tovary in accordance with changes in the variable resistance element.

Assuming that the output voltage of rectifier 29 across voltage divider3! increases, the voltage across voltage divider segment 3l-a willincrease proportionately; this increase will be amplified in amplifier32 and thence presented as an increasingly positive voltage to thecontrol grid of thermionic discharge'tube ii. A rise instead of a dropat the control grid of thermionic discharge tube 4 as a result of anassumed volt age increase may be accomplished, for example, by amplifier32 having an even number of concatenated stages. The assumed increase inthe control grid voltage of discharge tube 4 will reduce the resistancepresented between points I) and a by the variable resistance element andwill increase the current drawn through the fixed impedance 23 by thelatter. The increase of current through fixed impedance 28 increases thevoltage drop across it and reduces the voltage supplied to thetransformer 21 and therefore to the input vertices of the rectifier 29.The originally assumed increase in output voltage will thus beminimized.

Similarly, it may be shown that a decrease in output voltage willproduce a higher resistance between points 73 and a of the variableresistance element, reducing the drop across fixed impedance 28 andraising the output voltage across rectifier 29.

The transformer 27, inserted between the variable resistance element andthe rectifier 29, will isolate direct currents between the latter twoelements, assisting in the operation of the direct coupled amplifier 32.

Referring now to Fig. i a source of alternating voltage is supplied toterminals H and 12. The primary of transformer 33 is connected in serieswith the variable resistance element between points a and b to thesupply terminals II and 52. The secondary of transformer-33 connects tothe input vertices of a conventional rectifier t l. Again, thisrectifier 3 3 is shown as a full wave, metallic disc rectifier, but manytypes of rectifier systems may be employed. The output vertices ofrectifier 3d are supplied in series with a fixed resistance to a loadcircuit 36. Increases or decreases in magnitude of the load current fromrectifier 34 will be reflected as increased and decreased voltage dropsacross the resistance 35. As with transformer 21, transformer 33provides the function of isolating the direct currents of the system andadjustin the desired output voltage.

For example, an increase in the output current will reflect anincreasing voltage drop across resistance 35 and this increasing voltagemay be translated and amplified by amplifier 37 to provide a morenegative grid voltage to thermionic discharge tube a. The increasinglynegative grid voltage of thermionic discharge tube 6 will increase theresistance presented by the variable resistance element between points aand b; the alternating voltage supplied to the input vertices ofrectifiers 34 will be lowered, reducing the output current andcompensating for the originally assumed increase in output current.

Similarly, it may be shown that a reduction in the output current ofrectifier 34 will produce a corresponding decrease in the resistancepresented by the variable resistance element between points a and b,compensating for the originally assumed load current drop.

While the circuit with reference to Fig. 3 has been shown as providingconstant output voltage regulation, and with respect to Fig. 4, has been8 shown as providing constant output current regulation, it will beobvious to those skilled in the art that either constant output voltageorconstant output current may be maintained by an appropriate choice ofvoltage dividers or series lead resistances in either circuit as shown.

It is obvious that the scope of the invention is not limited to thespecific embodiments described, and that the invention may be employedin arrangements other than those given by way of example.

What is claimed is:

1. In an electric regulator apparatus for regulating the flow of asource of alternating current in series with an impedance, the circuitcomprising, a plurality of unidirectional conductors coupled in a fullwave bridge and having input and output vertices, means to couple theinput vertices of said bridge in series with the source of alternatingcurrent and impedance, a thermionic discharge tube having a cathode,anode and grid, means to couple the anode-cathode circuit of the saidthermionic discharge tube to the output vertices of the said bridge,means to derive a signal voltage having a magnitude varying according toa portion of the fiow of the said source of alternating current, andmeans to couple the said signal voltage to the control grid-cathodecircuit of the said thermionic discharge tube.

2. In a rectifier having a grid-controlled gaseous discharge tube andenergizing circuits therefor, a regulator comprising a phase shiftingcircuit having means to derive an alternating potential having twocomponents with displaced phase relation, means to vary the magnitude ofone of the components, said latter means comprising a plurality ofasymmetrically conducting varistors connected as a full wave bridge andhaving input vertices and a positive and negative output vertex, 2.thermionic discharge tube having an anode, cathode and grid, means toconnect the positive and negative output vertices of the said varistorbridge to the said anode and cathode, respectively, means to apply thesaid alternating potential to the grid of the gaseous discharge tube,means to derive a signal voltage varying in accordance with the outputof the gaseous discharge tube, and means to impress the said signalvoltage on the grid-cathode circuit of the said thermionic dischargetube.

3. In a direct current power supply system having a grid-controlledgaseous discharge tube and energizing circuits therefor to supply adirect current to a load from a source of alternating current, theregulator comprising, a phase shifting circuit having means to derive afirst alternating potential component in phase with the source ofalternating current and a second alternating potential component indisplaced phase with the said source of alternating current, means tovary the magnitude of the first said component, said latter meanscomprising first, second, third and fourth asymmetrically conductingvaristors connected as a full wave bridge and having input vertices anda positive and negative output vertex, a thermionic discharge tubehaving an anode, cathode and grid, means to connect the positive andnegative output vertices of the said varistor bridge to the said anodeand cathode, respectively, means to combine the said two potentialcom-ponents vecto'rially and to supply the vectorial sum to the grid ofthe gaseous discharge tube, means to derive a signal voltage varying inaccordance with a portion of the output voltage of the gaseous dischargetube, and means to impress the said signal voltage on the grid-cathodecircuit of the said thermionic discharge tube.

4. In a direct current power supply system having a grid-controlledgaseous discharge tube and energizing circuits therefor to supply adirect current to a load from a source of alternating current, theregulatorcomprising, a phase shifting circuit having means to derive afirst alternating potential component in phase with the source ofalternating current and a second alternating potential component indisplaced phase with the said source of alternating current, means tovary the magnitude of the first said component, said latter meanscomprising first, second, third and fourth asymmetrically conductingvaristors connected as a full wave bridge and having input vertices anda positive and negative output vertex, a thermionic discharge tubehaving an anode, cathode and grid, means to connect the positive andnegative output vertices of the said varistor bridge to the said anodeand cathode, respectively, means to combine the said two potentialcomponents vectorially and to supply the vectorial sum to the grid ofthe gaseous discharge tube, means to derive a signal voltage varying inaccordance with a portion of the output current of the gaseous dischargetube, and means to impress the said signal voltage on the grid-cathodecircuit of the said thermionic discharge tube.

5. In a direct current power supply system including first and secondgrid-controlled gaseous discharge rectifiers having each a cathode, gridand anode for supplying a direct current to a load from a source ofalternating current having a given phase, said alternating current beingapplied to the anode-cathode circuits of the said rectifiers inpush-pull, the regulator circuit comprising, a transformer having asplit secondary winding and a primary winding connected to the source ofalternating current, means to derive a current in phase quadrature withthe source of alternating current, said latter means comprising areactance in series with a portion of the secondary of the saidtransformer, means to derive a variable current in phase with thealternating source, said latter means comprising first, second, thirdand fourth asymmetrically conducting varistors connected in a full Wavebridge and having input vertices and positive and negative outputvertices, a thermionic discharge tube having a cathode, grid and anode,means to connect the positive and negative output vertices of the saidvaristor bridge to the said anode and cathode, respectively, and meansto connect the input vertices of the varistor bridge in series with thefree portion of the secondary of the said transformer to provide thesaid variable current, means to derive a voltage resultant from thevectorial sum of the said phase quadrature and variable in-phasecurrents, means to supply the derived voltage to the grid-cathodecircuit of the grid-controlled gaseous discharge rectifiers inpush-pull, means to derive a control voltage in accordance with theoutput of the said grid-controlled gaseous discharge rectifiers, andmeans to apply the said derived control voltage to the grid-cathodecircuit of the said thermionic discharge tube.

6. In a power supply system according to claim wherein the said means toderive a control voltage includes means responsive selectively to theoutput voltage and load current of the said grid-controlled gaseousdischarge rectifiers.

7. In a power supply system according to claim 5 including a pluralityof thermionic discharge tubes having each a cathode, grid and anode,means to couple the said plurality of thermionic discharge tubestogether in parallel and in parallel with the said first-mentionedthermionic discharge tube.

8. In a power supply having a, rectifier for providing'direct currentoutput to a load from an input source of alternating current, aregulating circuit comprising, a plurality of unidirectional conductorsconnected as a full Wave bridge and having input vertices and positiveand negative output vertices, a space current device having an anode,cathode and control electrode, means for connecting the positive andnegative output vertices of the said bridge respectively to the anodeand cathode of the said space current device, an impedance, directcurrent isolating means to couple the input vertices of the said bridgein parallel with the rectifier input, means to couple the input verticesof the said bridge in series with the said impedance and source ofalternating current, means to derive a signal voltage varying in accordwith the output of the rectifier, and means for impressing the saidsignal voltage on the control electrode of the said space currentdevice.

9. In a power supply having a rectifier for providing direct currentoutput to a load from an input source of alternating current, aregulating circuit comprising, a first, a second, a third and a fourthasymmetrically conducting varistor connected as a full wave bridge andhaving input vertices and positive and negative output vertices, athermionic discharge tube having an anode, cathode and grid, means forconnecting the positive and negative output vertices of the said bridgerespectively to the anode and cathode of the said thermionic dischargetube, an impedance, transformer means to couple the input vertices ofthe said bridge in parallel with the rectifier input, means to couplethe input vertices of the said bridge in series with the said impedanceand source of alternating current, means to derive a signal voltageresponsive selectively to the output voltage and load current of therectifier, and means for impressing the said signal voltage on the gridof the said thermionic discharge tube.

10. In a power supply having a rectifier for providing direct currentoutput to a load from an input source of alternating current, aregulating circuit comprising, a plurality of unidirectional conductorsconnected as a full wave bridge and having input vertices and positiveand negative output vertices, a space current device having an anode,cathode and control electrode, means for connecting the positive andnegative output vertices of the said bridge re-. spectively to the anodeand cathode of the said space current device, means to couple the inputvertices of the said bridge in series with the rectifier input and thesource of alternating current, means to derive a signal voltageresponsive to the output of the rectifier, and means for impressing thesaid signal voltage on the control electrode of the said space currentdevice.

11. In a power supply system according to claim 10 wherein the saidmeans to couple the input vertices of the said bridge in series with therectifier input and the source of alternating current includes a directcurrent isolation transformer interposed between the input vertices ofthe said bridge and the rectifier.

12. In a power supply having a rectifier for providing direct currentoutput to a load'from 11 a source of alternating current, a regulating'circuit comprising a first, a second, a third and a fourthasymmetrically conducting varistor connected as a full wave bridge andhaving input vertices and positive and negative output vertices, athermionic discharge tube having an anode, cathode and grid, means forconnecting the positive and negative output vertices of the said bridgerespectively to the anode and cathode of the said thermionic dischargetube, means to couple the input vertices of the said bridge in serieswith the rectifier input and the source of alternating current, means toderive a signal voltage responsive selectively to the output volt-REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name .Date

2,095,827 Moyer Oct. 12, 1-937 2,316,008 Ludbrook Apr. 6, 19%

